1. Field of the Invention
The present invention relates to a bone evaluation method. More specifically, it relates to a bone evaluation method in which a cancellous bone is evaluated based on a bone density pattern (i.e. a graph obtained through scanning the bone or the X-ray film and plotting the intensity of transmitted photon beam or X-ray) of the cancellous bone. For the evaluation of bones, the bone density pattern is transformed to power spectrum through the algorithm of the Fourier transformation or is processed to calculate the parameters of bone atrophy such as the area (.SIGMA.GS) of the bone density pattern and/or the value (.SIGMA.GS/D) obtained by dividing the area (.SIGMA.GS) by the bone width (D).
2. Description of the Related Art
The human bones are generally subdivided into cortical bone and cancellous bone. The cortical bone is dense osseous tissue and is represented by the diaphysis of appendicular skelton in the form of pipes. On the other hand, cancellous bone consists mainly of trabeculae. Such cancellous bone is present, for example, in the epiphysial portions of long shaft bones, vertebrae, carpal bones, calcanei, tali, and tarsal bones. However, since cancellous bone has a larger surface in contact with soft tissue containing vasculatures, cancellous bone shows higher metabolic turn over and is predisposed to rapid changes under bone diseases or treatments.
The so-called MD method is known as a method for evaluating cortical bones, for example, growth conditions of human skelton, bone age, or kinds of bone diseases such as osteoporosis and osteomalacia, as disclosed in, for example, "Kotsu Taisha" (i.e., Bone Metabolism) 13, pp 187-195 (1980) and 14, pp 91-104, (1981). The improved MD method is disclosed in, for example, "Kotsu Keitai Keisoku" (i.e., "Bone Morphometry") 5, 36-46 (1983).
On the other hand, a method is known of evaluating the cancellous bone whereby the bone is evaluated by analysing changes in the trabeculae from a plane X-ray of the cancellous bone. That is, the distribution of the trabeculae of the cancellous bone depends upon the stress distribution applied to the bones, and bones contain thick trabeculae supporting the body weight (i.e., principal trabeculae) as well as thin trabeculae linking the thick trabeculae (i.e., subtrabeculae). When the bone volume is decreased due to diseases such as osteoporosis, commonly the subtrabeculae are first absorbed and the principal trabeculae are retained in a relatively good condition. Accordingly, various methods for evaluating the degree of bone atrophy were developed utilizing the above-mentioned common occurrence. For example, the Itami's classification for the spine, the Singh's classification for the neck of the femur, and the so-called calcaneal index for calcanei are known (see Osteoporosis (Kiso and Rinsho), T. Fujita et al, pages 331-337; published on Nov., 1983 by Kyowakikaku Tsushin; J. Bone and Joint Surg., Vol. 65 B, No. 2, p 195-198 (1983); and J. Bone and Joint Surg., Vol. 52 A, 457 (1970)).
However, all these methods evaluate the degree of bone atrophy by the visual observation of plane X-ray photographs and, therefore, are unsatisfactory from an objective standpoint. Furthermore, the accuracy of these methods is insufficient to distinguish minor changes in the bone diseases, and thus, there is a strong need to develop a method for objectively and quantitatively evaluating the conditions of cancellous bone.